// PointLightedCube_perFragment.js (c) 2012 matsuda
// Vertex shader program
var VSHADER_SOURCE =
  `attribute vec4 a_position;
  attribute vec4 a_normal;
  attribute vec2 a_TexCoord;
  uniform vec3 u_lightWorldPosition;  // 光源位置

  uniform mat4 u_world;    // Model matrix
  uniform mat4 u_worldViewProjection;
  uniform mat4 u_worldInverseTranspose;   // Transformation matrix of the normal

  varying vec3 v_normal;
  varying vec3 v_surfaceToLight;
  varying vec2 v_TexCoord;
  
  void main() {
    // 将位置和矩阵相乘
    gl_Position = u_worldViewProjection * a_position + vec4(0, 0, 0, 1.0);

    // 重定向法向量并传递到片断着色器
    v_normal = normalize(vec3(u_worldInverseTranspose * a_normal));

    // 计算表面的世界坐标
    vec3 surfaceWorldPosition = vec3(u_world * a_position);

    // 计算表面到光源的方向
    // 然后传递到片断着色器
    v_surfaceToLight = u_lightWorldPosition - surfaceWorldPosition;

    v_TexCoord = a_TexCoord;
  }`;

// Fragment shader program
var FSHADER_SOURCE =
  `#ifdef GL_ES
  precision mediump float;
  #endif

  uniform float u_shininess;
  uniform vec3 u_lightColor;
  uniform vec3 u_specularColor;
  uniform sampler2D u_Sampler;
  uniform vec3 u_AmbientLight;
  varying vec3 v_normal;
  varying vec3 v_surfaceToLight;
  // varying vec4 v_color;
  varying vec2 v_TexCoord;

  void main() {
    // 由于 v_normal 是可变量，所以经过插值后不再是单位向量，
    // 单位化后会成为单位向量
    vec3 normal = normalize(v_normal);
   
    vec3 surfaceToLightDirection = normalize(v_surfaceToLight);
   
    vec3 halfVector = normalize(surfaceToLightDirection);
    float light = dot(normal, surfaceToLightDirection);

    float specular = 0.0;
    if (light > 0.0) {
      specular = pow(dot(normal, halfVector), u_shininess);
    }
    
    vec4 color = texture2D(u_Sampler, v_TexCoord) ;
   
    // 只将颜色部分（不包含 alpha） 和光照相乘
    color.rgb *= light*u_lightColor;
   
    // 直接和高光相加
    color.rgb += specular * u_specularColor;

    // 设置环境光
    vec3 diffuse = u_lightColor * color.rgb * light;
    vec3 ambient = u_AmbientLight * color.rgb;
    vec4 v_Color = vec4(diffuse + ambient, color.a);

    gl_FragColor = v_Color;
  }`;

function main() {
  // Retrieve <canvas> element
  var canvas = document.getElementById('webgl');

  // Get the rendering context for WebGL
  var gl = getWebGLContext(canvas);
  if (!gl) {
    console.log('Failed to get the rendering context for WebGL');
    return;
  }

  // Initialize shaders
  if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
    console.log('Failed to intialize shaders.');
    return;
  }

  // 
  var n = initVertexBuffers(gl);
  if (n < 0) {
    console.log('Failed to set the vertex information');
    return;
  }

  // Set the clear color and enable the depth test
  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.enable(gl.DEPTH_TEST);

  // Get the storage locations of uniform variables
  var u_world = gl.getUniformLocation(gl.program, 'u_world');
  var u_worldViewProjection = gl.getUniformLocation(gl.program, 'u_worldViewProjection');
  var u_worldInverseTranspose = gl.getUniformLocation(gl.program, 'u_worldInverseTranspose');
  var u_lightWorldPosition = gl.getUniformLocation(gl.program, 'u_lightWorldPosition');
  var lightColor = gl.getUniformLocation(gl.program, "u_lightColor");
  var specularColorLocation = gl.getUniformLocation(gl.program, "u_specularColor");
  var shininessLocation = gl.getUniformLocation(gl.program, "u_shininess");
  var u_AmbientLight = gl.getUniformLocation(gl.program, 'u_AmbientLight');
  if (!u_world || !u_worldViewProjection || !u_worldInverseTranspose  || !u_lightWorldPosition || !u_AmbientLight) { 
    console.log('Failed to get the storage location');
    return;
  }
  
  gl.uniform3f(u_AmbientLight, 0.2, 0.2, 0.2);

  //设置光源位置
  gl.uniform3f(u_lightWorldPosition, 0, 6, 0);
  // 设置光照颜色
  gl.uniform3f(lightColor, 1, 1, 1); 
  // 设置高光颜色
  gl.uniform3f(specularColorLocation, 1, 1, 1);
  // 设置亮度
  gl.uniform1f(shininessLocation, 200);


  var modelMatrix = new Matrix4();  // Model matrix
  var mvpMatrix = new Matrix4();    // Model view projection matrix
  var normalMatrix = new Matrix4(); // Transformation matrix for normals
  var currentAngle = 0.0;  // Current rotation angle

  var tick = function() {
    currentAngle = animate(currentAngle);  // Update the rotation angle

    // Calculate the model matrix
    modelMatrix.setRotate(currentAngle, 0, 1, 0); 
    // Calculate the view projection matrix
    mvpMatrix.setPerspective(60, 1, 1, 100);
    mvpMatrix.lookAt(0.0, 8.0, 8.0, 0, 2, 0, 0, 1, 0);
    mvpMatrix.multiply(modelMatrix);
    // Calculate the matrix to transform the normal based on the model matrix
    normalMatrix.setInverseOf(modelMatrix);
    normalMatrix.transpose();

    initTextures(gl, n);

    // Pass the model matrix to u_world
    gl.uniformMatrix4fv(u_world, false, modelMatrix.elements);

    // Pass the model view projection matrix to u_worldViewProjection
    gl.uniformMatrix4fv(u_worldViewProjection, false, mvpMatrix.elements);

    // Pass the transformation matrix for normals to u_worldInverseTranspose
    gl.uniformMatrix4fv(u_worldInverseTranspose, false, normalMatrix.elements);

    // Clear color and depth buffer
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    // Draw the cube
    gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);

    requestAnimationFrame(tick, canvas); // Request that the browser ?calls tick
  };
  tick();
}

function initVertexBuffers(gl) {
  // Create a cube
  //    v6----- v5
  //   /|      /|
  //  v1------v0|
  //  | |     | |
  //  | |v7---|-|v4
  //  |/      |/
  //  v2------v3
  // Coordinates
  var vertices = new Float32Array([
     2.0, 2.0, 2.0,  -2.0, 2.0, 2.0,  -2.0,-2.0, 2.0,   2.0,-2.0, 2.0, // v0-v1-v2-v3 front
     2.0, 2.0, 2.0,   2.0,-2.0, 2.0,   2.0,-2.0,-2.0,   2.0, 2.0,-2.0, // v0-v3-v4-v5 right
     2.0, 2.0, 2.0,   2.0, 2.0,-2.0,  -2.0, 2.0,-2.0,  -2.0, 2.0, 2.0, // v0-v5-v6-v1 up
    -2.0, 2.0, 2.0,  -2.0, 2.0,-2.0,  -2.0,-2.0,-2.0,  -2.0,-2.0, 2.0, // v1-v6-v7-v2 left
    -2.0,-2.0,-2.0,   2.0,-2.0,-2.0,   2.0,-2.0, 2.0,  -2.0,-2.0, 2.0, // v7-v4-v3-v2 down
     2.0,-2.0,-2.0,  -2.0,-2.0,-2.0,  -2.0, 2.0,-2.0,   2.0, 2.0,-2.0  // v4-v7-v6-v5 back
  ]);

  var texCoords = new Float32Array([
    1.0, 1.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
    0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 1.0, 1.0,
    1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 0.0, 0.0,
    1.0, 1.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
    0.0, 0.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0,
    0.0, 0.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0
]);

  // Colors
//   var colors = new Float32Array([
//     1, 0, 0,   1, 0, 0,   1, 0, 0,  1, 0, 0,     // v0-v1-v2-v3 front
//     1, 0, 0,   1, 0, 0,   1, 0, 0,  1, 0, 0,     // v0-v3-v4-v5 right
//     1, 0, 0,   1, 0, 0,   1, 0, 0,  1, 0, 0,     // v0-v5-v6-v1 up
//     1, 0, 0,   1, 0, 0,   1, 0, 0,  1, 0, 0,     // v1-v6-v7-v2 left
//     1, 0, 0,   1, 0, 0,   1, 0, 0,  1, 0, 0,     // v7-v4-v3-v2 down
//     1, 0, 0,   1, 0, 0,   1, 0, 0,  1, 0, 0　    // v4-v7-v6-v5 back
//  ]);

  // Normal
  var normals = new Float32Array([
    0.0, 0.0, 1.0,   0.0, 0.0, 1.0,   0.0, 0.0, 1.0,   0.0, 0.0, 1.0,  // v0-v1-v2-v3 front
    1.0, 0.0, 0.0,   1.0, 0.0, 0.0,   1.0, 0.0, 0.0,   1.0, 0.0, 0.0,  // v0-v3-v4-v5 right
    0.0, 1.0, 0.0,   0.0, 1.0, 0.0,   0.0, 1.0, 0.0,   0.0, 1.0, 0.0,  // v0-v5-v6-v1 up
   -1.0, 0.0, 0.0,  -1.0, 0.0, 0.0,  -1.0, 0.0, 0.0,  -1.0, 0.0, 0.0,  // v1-v6-v7-v2 left
    0.0,-1.0, 0.0,   0.0,-1.0, 0.0,   0.0,-1.0, 0.0,   0.0,-1.0, 0.0,  // v7-v4-v3-v2 down
    0.0, 0.0,-1.0,   0.0, 0.0,-1.0,   0.0, 0.0,-1.0,   0.0, 0.0,-1.0   // v4-v7-v6-v5 back
  ]);

  // Indices of the vertices
  var indices = new Uint8Array([
     0, 1, 2,   0, 2, 3,    // front
     4, 5, 6,   4, 6, 7,    // right
     8, 9,10,   8,10,11,    // up
    12,13,14,  12,14,15,    // left
    16,17,18,  16,18,19,    // down
    20,21,22,  20,22,23     // back
 ]);

  // Write the vertex property to buffers (coordinates, colors and normals)
  if (!initArrayBuffer(gl, 'a_position', vertices, 3)) return -1;
  if (!initArrayBuffer(gl, 'a_normal', normals, 3)) return -1;
  if (!initArrayBuffer(gl, 'a_TexCoord', texCoords, 2)) return -1;
  // Unbind the buffer object
  gl.bindBuffer(gl.ARRAY_BUFFER, null);

  // Write the indices to the buffer object
  var indexBuffer = gl.createBuffer();
  if (!indexBuffer) {
    console.log('Failed to create the buffer object');
    return false;
  }
  gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
  gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);

  return indices.length;
}

function initArrayBuffer(gl, attribute, data, num) {
  // Create a buffer object
  var buffer = gl.createBuffer();
  if (!buffer) {
    console.log('Failed to create the buffer object');
    return false;
  }
  // Write date into the buffer object
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);
  // Assign the buffer object to the attribute variable
  var a_attribute = gl.getAttribLocation(gl.program, attribute);
  if (a_attribute < 0) {
    console.log('Failed to get the storage location of ' + attribute);
    return false;
  }
  gl.vertexAttribPointer(a_attribute, num, gl.FLOAT, false, 0, 0);
  // Enable the assignment of the buffer object to the attribute variable
  gl.enableVertexAttribArray(a_attribute);

  return true;
}

// Rotation angle (degrees/second)
var ANGLE_STEP = 30.0;
// Last time that this function was called
var g_last = Date.now();
function animate(angle) {
  // Calculate the elapsed time
  var now = Date.now();
  var elapsed = now - g_last;
  g_last = now;
  // Update the current rotation angle (adjusted by the elapsed time)
  var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0;
  return newAngle %= 360;
}

function initTextures(gl, n) {
  var texture = gl.createTexture();
  var u_Sampler = gl.getUniformLocation(gl.program, 'u_Sampler');
  var image = new Image();
  image.onload = function () {
      onLoadTexture(gl, n, texture, u_Sampler, image);
  };
  image.src = "../resources/img.png";
  return true;
}

function onLoadTexture(gl, n, texture, u_Sampler, image) {
  gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, 1);
  gl.activeTexture(gl.TEXTURE0);
  gl.bindTexture(gl.TEXTURE_2D, texture);// 绑定纹理对象到激活的纹理单元
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);// 纹理放大方式
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);// 纹理缩小方式
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);// 纹理水平填充方式
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);// 纹理垂直填充方式
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, gl.RGB, gl.UNSIGNED_BYTE, image);
  gl.uniform1i(u_Sampler, 0);
  gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
  gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);
}